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PubMed1998

Blockade of very late antigen-4 integrin binding to fibronectin in allograft recipients: I. Treatment with connecting segment-1 peptides prevents acute rejection by suppressing intragraft mononuclear cell accumulation, endothelial activation, and cytokine expression.

BACKGROUND: Allograft rejection is associated with infiltration of inflammatory cells and local deposition of fibronectin (FN). This study was carried out to examine the hypothesis that peptides known to specifically block adhesive interactions between the connecting segment-1 (CS1)-binding domain of FN and alpha4beta1 integrin on circulating cells may interfere with the immune cascade, which would lead to acute rejection in transplant recipients. METHODS AND RESULTS: Cardiac allografts from Lewis x Brown Norway F1 hybrids were rejected in 7+/-1 days in Lewis rats. Treatment with bioactive CS1 peptides (4 mg/kg/day i.v. for 7 days) abrogated acute rejection and prolonged cardiac allograft survival to 13+/-1 days (P<0.001). This effect correlated with decreased expression of total fibronectin and cell adhesion molecules, such as alpha4beta1, vascular cell adhesion molecule-1, intercellular adhesion molecule-1, as well as reduced infiltration by CD4+ and CD8+ T cells at the graft site. Treatment with CS1 peptides decreased alloantigen activation, as evidenced by decreased intragraft infiltration by CD25+ cells, and diminished expression of mRNA coding for Th1 (interleukin [IL]-2, interferon-gamma)- and Th2 (IL-4, IL-5, IL-6)-type cytokines. CS1-mediated immunosuppressive effects could be reversed and acute rejection recreated after adjunctive treatment of rats with recombinant IL-2. CONCLUSION: Our data are consistent with the model in which in vivo interaction between the alpha4beta1 integrin receptor and the cell-associated CS1 motif of FN is critical for rejection cascade. The novel therapeutic approach of selectively blocking the alpha4beta1-FN activation pathway with CS1 peptides prevents acute allograft rejection by inhibiting expansion of antigen-specific T cells and inducing a transient state of cytokine-responsive anergy in the residual T-cell population.

Amino Acid Sequence↗

PubMed2003

Structural characterization of hellethionins from Helleborus purpurascens.

Thionins are relatively small-sized multiple-cystine peptides that are probably involved in the plant defense against pathogens. As such, these peptides constitute promising candidates for engineered plant resistance in the agricultural industry. More recently, thionins have been proposed as potential immunotoxins in tumor therapy. In the search for pharmacologically active natural products, a new family of thionins was recently discovered in the roots of Helleborus purpurascens that accordingly were termed hellethionins. The structural characterization by NMR of one representative member of this family, i.e., of hellethionin D, clearly reveals that thionins from different sources share a highly conserved overall fold. In fact, the well-defined 3D structure of hellethionin D is very similar to those reported so far for viscotoxins, purothionins, or crambin, although distinct differences could be detected in the C-terminal portion, especially for loop 36-39. These differences may derive from the unusual distribution of charged residues in the C-terminal half of the peptide sequence compared to other thionins and from the uncommon occurrence of four contiguous threonine residues in loop 36-39. As expected, reduction of the disulfide bonds in hellethionin D leads to complete unfolding, but upon oxidative refolding by air oxygen in the presence of glutathione the correct isomer is recovered in high yields, confirming the very robust fold of this class of bioactive cystine peptides.

Amino Acid Sequence↗

PubMed2004

A novel peptide modulates alpha7 nicotinic receptor responses: implications for a possible trophic-toxic mechanism within the brain.

The alpha7 nicotinic acetylcholine receptor (nAChR) plays a key role in neural development and neurodegeneration. Here, we identify a novel, modulatory receptor ligand, a 14-amino acid peptide (AEFHRWSSYMVHWK) derived from the C-terminus of acetylcholinesterase (AChE). In three different in vitro preparations, this 'AChE-peptide' is bioactive in a ligand-specific and concentration-dependent manner. First, it modulates acutely the effect of acetylcholine (ACh) on Xenopus oocytes transfected with human alpha7, but not alpha4/beta2, nAChR. The action persists when intracellular calcium is chelated with BAPTA or when calcium is substituted with barium ions. This observation suggests that intracellular Ca(2+) signals do not mediate the interaction between the peptide and nAChR, but rather that the interaction is direct: however, the intervention of other mediators cannot be excluded. Secondly, in recordings from the CA1 region in guinea-pig hippocampal slices, AChE-peptide modulates synaptic plasticity in a alpha-bungarotoxin (alpha-BgTx)-sensitive manner. Thirdly, in organotypic cultures of rat hippocampus, long-term exposure to peptide attenuates neurite outgrowth: this chronic, functional effect is selectively blocked by the alpha7 nAChR antagonists, alpha-BgTx and methyllycaconitine, but not by the alpha4/beta2-preferring blocker dihydro-beta-ethroidine. A scrambled peptide variant, and the analogous peptide from butyrylcholinesterase, are ineffective in all three paradigms. The consequences of this novel modulation of the alpha7 nAChR may be activation of a trophic-toxic axis, of relevance to neurodegeneration.

Acetylcholine↗

PubMed1999

Differential regulation of peptide alpha-amidation by dexamethasone and disulfiram.

alpha-Amidation is essential for the function of many peptides in intercellular communication. This C-terminal modification is mediated in a two-step process by the hydroxylase and lyase activities of the bifunctional enzyme, peptidylglycine alpha-amidating monooxygenase (PAM). The first step, catalyzed by peptidylglycine-alpha-hydroxylating monooxygenase (PHM; EC 1.14.17. 3), is rate limiting in the process, and therefore subject to regulation. Dexamethasone and disulfiram (tetraethylthiuram disulfide; Antabuse) were used as in vivo treatments to study the regulation of PHM expression and activity in cardiac atrium. Our findings show that both dexamethasone and disulfiram treatment increase the activity of PHM in atrial tissue but that they do so by distinctly different mechanisms. Dexamethasone elevated tissue levels of PAM mRNA and protein concurrently, suggesting that glucocorticoids regulate PAM expression at the level of gene transcription. In contrast, disulfiram treatment, which depletes stores of alpha-amidated peptides, increased the specific activity of PHM without affecting the level of PAM expression. The catalytic efficiency of PHM was enhanced by raising the Vmax of the enzyme. Importantly, this increase in Vmax was retained through purification to homogeneity, indicating that either a covalent modification or a stable conformational change had occurred in the protein. These novel findings demonstrate that the rate-limiting enzyme in the bioactivation of peptide messengers is differentially regulated by transcriptional and post-transcriptional mechanisms in vivo. It is proposed that regulation of PHM's expression and catalytic efficiency serve as coordinated physiologic mechanisms for maintaining appropriate levels of alpha-amidating activity under changing conditions in vivo.

Animals↗

PubMed1996

Reversed-phase high-performance liquid chromatography coupled with second-order derivative spectroscopy for the quantitation of aromatic amino acids in peptides: application to hemorphins.

The characterization of aromatic amino acid-containing peptides in biological fluids or protein hydrolysates is commonly achieved using classical size-exclusion (SE) and reversed-phase (RP) high-performance liquid chromatography (HPLC) coupled with direct ultraviolet (UV) spectrometry. Here, a non-destructive quantitative determination of aromatic amino acids in peptides is developed using second-order derivative spectra obtained during RP-HPLC coupled with photodiode array detection. In this method, the free aromatic amino acids were used as standards. Sensitivity and accuracy were verified using some peptides, including bioactive hemorphins. The method was applied to determine the amounts of hemorphins present in a complex peptic bovine hemoglobin hydrolysate.

Amino Acid Sequence↗

PubMed2006

Processing of cocaine- and amphetamine-regulated transcript (CART) precursor proteins by prohormone convertases (PCs) and its implications.

Cocaine- and amphetamine-regulated transcript (CART) peptides are expressed in several neuroendocrine tissues, including hypothalamus, pituitary, gut, adrenal and pancreas, and are involved in regulating important biological processes including feeding/appetite, drug reward and stress. CART is synthesized as larger, inactive peptide precursors (pro-CART) that require endoproteolytic processing to generate smaller, active forms. Prohormone/proprotein convertases (PCs), a family of calcium-dependent, serine endoproteases, have been shown to cleave many protein precursors in the regulated/constitutive secretory pathway to generate smaller fragments. In our previous studies, we have demonstrated the important roles of the two neuroendocrine-specific PCs, PC2 and PC1/3, in processing the two pro-CART isoforms, long (102aa) and short (89aa), to generate the bioactive CART peptides, I (55-102/42-89) and II (62-102/49-89) as well as the intermediate fragments, 10-89 and 33-102. Our subsequent studies have revealed the participation of another PC family member, PC5/6A (the soluble isoform of a widely expressed PC, PC5/6), in cleaving both precursor isoforms. We conclude that PC5/6A contributes to the normal efficient processing of pro-CART and is functionally more redundant with PC2 than PC1/3 in generating both CART I and II.

Animals↗

PubMed1997

Bioactive fragment of human IL-1beta [163-171] modulates the immune response to synthetic peptides of HIV.

The activation of T helper cells specific for viral antigens is critical for antibody production and the generation of cytotoxic T cells during retroviral infection. In this study, we examined the effect of linking HIV peptides with a bioactive fragment of human interleukin-1beta (IL-1beta) (163-171) on the induction of immune response to the peptides. A panel of highly purified synthetic peptides representing defined regions of gp41, Gag and gp120 were used as antigens. Mouse spleen cells primed with the peptide conjugates produced greater proliferation on in vitro stimulation than spleen cells primed with peptide alone. In addition, antibody production as assessed by ELISA was observed after immunization with conjugated peptides but not with peptide alone, indicating B-cell activation. We also found that a high level of IgG2a antibody production correlated with a high level of IFN-gamma production. These findings favor the notion that IL-1beta plays an important role in immune responses. These observations support the formulation and design of synthetic vaccines against HIV using synthetic HIV peptides conjugated with immunomodulators. Such an approach may provide an effective vaccination against other infectious agents.

AIDS Vaccines↗

PubMed1999

What peptides these deltorphins be.

The deltorphins are a class of highly selective delta-opioid heptapeptides from the skin of the Amazonian frogs Phyllomedusa sauvagei and P. bicolor. The first of these fascinating peptides came to light in 1987 by cloning of the cDNA of from frog skins, while the other members of this family were identified either by cDNA or isolation of the peptides. The distinctive feature of deltorphins is the presence of a naturally occurring D-enantiomer at the second position in their common N-terminal sequence, Tyr-D-Xaa-Phe, comparable to dermorphin, which is the prototype of a group of mu-selective opioids from the same source. The D-amino acid and the anionic residues, either Glu or Asp, as well as their unique amino acid compositions are responsible for the remarkable biostability, high delta-receptor affinity, bioactivity and peptide conformation. This review summarizes a decade of research from many laboratories that defined which residues and substituents in the deltorphins interact with the delta-receptor and characterized pharmacological and physiological activities in vitro and in vivo. It begins with a historical description of the topic and presents general schema for the synthesis of peptide analogues of deltorphins A, B and C as a means to document the methods employed in producing a myriad of analogues. Structure activity studies of the peptides and their pharmacological activities in vitro are detailed in abundantly tabulated data. A brief compendium of the current level of knowledge of the delta-receptor assists the reader to appreciate the rationale for the design of these analogues. Discussion of the conformation of these peptides addresses how structure leads to further hypotheses regarding ligand receptor interaction. The review ends with a broad discussion of the potential applications of these peptides in clinical and therapeutic settings.

Amino Acid Sequence↗

PubMed1998

The Ewing tumor family of peripheral primitive neuroectodermal tumors expresses human gastrin-releasing peptide.

The Ewing tumor family of peripheral primitive neuroectodermal tumors (pPNETs) are characterized by chromosomal translocations leading to EWS-ETS gene fusions. These hybrid genes express chimeric proteins that are thought to act as aberrant transcription factors. We therefore used differential display-PCR to compare gene expression patterns in pPNET cell lines with those of other small round cell tumors (SRCTs) of childhood. This technique detected differential expression of sequences corresponding to human gastrin-releasing peptide (GRP) in pPNET cell lines but not in other SRCT cell lines. Subsequent Northern and reverse transcription-PCR analysis of SRCT cell lines confirmed GRP positivity in all pPNET lines tested. Of primary tumors tested by reverse transcription-PCR, GRP expression was found in 7 (44%) of 16 pPNETs but in no other primary SRCTs examined. Expression of the GRP receptor gene was demonstrable in 55% of pPNET cell lines and 25% of primary pPNET tumors but also in several other SRCTs. Radioimmunoassays and immunohistochemistry confirmed expression of bioactive GRP peptide in pPNET cell lines and primary tumors, respectively. Moreover, in vitro growth of a pPNET cell line was slowed by treatment with a GRP receptor antagonist and accelerated by a GRP receptor agonist. GRP is a known autocrine growth factor in small cell lung cancer and other neuroendocrine tumors. Its expression in pPNETs provides further evidence for a neuroectodermal histogenesis of these tumors and suggests that autocrine growth of this family of tumors may be at least partially regulated by GRP.

Artificial Gene Fusion↗

PubMed2006

[Efficient expression and purification of human beta-defensin-2 in E.coli].

OBJECTIVE: To demonstrate the possibility of high-level expression of bioactive human beta-defensin-2 (hBD2) in E.coli, and to purify the recombinant hBD2. METHODS: DNA fragment containing mature hBD2 coding region (smhBD2-cDNA) was amplified by PCR, multiple copies of smhBD2-cDNA were linked using Bgl II and BamH I enzymes, pET32-nsmHBD2-cDNA with 1, 2, 4, or 8 copies of smhBD2-cDNA was constructed. The soluble and insoluble hBD2 proteins were separated and analyzed by SDS-PAGE analysis. The soluble protein underwent a separation process containing affinity chromatography, enterokinase digestion and ion exchange chromatography to get the recombinant hBD2 peptide. The bioactivity of recombinant hBD2 was examined by bacteria-inhibition tests in liquid culture. RESULT: The plasmids pET32-nsmHBD2-cDNA with 1, 2, 4 copies of smhBD2-cDNA were constructed and the expressed soluble protein accounted for 52 %, 48 %, and 31 % respectively. The plasmids with 8 copies expressed mainly insoluble protein with few in soluble form. The growth of E.coli K12D31 was dramatically suppressed with a inhibition rate of 90 %, when the final concentration of recombinant hBD2 reached between 0.4 to 0.5 mug/ml. CONCLUSION: Fusion expression of human beta-defensin-2 with multiple joined genes in E.coli could increase the expression of hBD2.

Anti-Infective Agents↗

PubMed2003

On the tissue-specific processing of procholecystokinin in the brain and gut--a short review.

Cholecystokinin (CCK) is a major peptide hormone in the gut and a major peptide transmitter in the brain. Its synthesis requires endoproteolytic cleavage of proCCK at several mono- and dibasic sites by prohormone convertases (PCs). Of these, PC1 and PC2 are expressed in cerebral neurons and intestinal endocrine cells. Characteristically, however, the processing of proCCK varies markedly between the brain and the gut. In neurons, CCK-8 is always the predominating form, whereas the endocrine gut cells (I-cells) contain a mixture of small and larger CCK-peptides of which CCK-33 or CCK-22 often predominate. The role of PC1 and PC2 in the processing of proCCK have now been examined by measuring the concentrations of prohormone, processing intermediates and amidated end-products in jejunal and cerebral extracts of PC1 and PC2 deficient mice and corresponding wild type controls. The PC1 null mice revealed a pattern opposite to that of the PC2 null mice, in whom only the cerebral processing of proCCK was affected. Thus PC1 knockouts reveal a severe block in the processing of intestinal proCCK. Accordingly, the intestinal concentration of proCCK was many fold increased, and also the concentrations of different processing intermediates were raised; but the concentration of bioactive, alpha-amidated and O-sulfated CCK was reduced to a few percent of normal. The only bioactive CCK peptide in the gut of PC1 deficient mice was CCK-22, and it was present only in trace amounts. The cerebral processing of proCCK was, however, not at all affected by the lack of PC1 - in sharp contrast to the effect of PC2. The results show that the tissue-specific processing of proCCK to a large extent can be explained by prohormone convertases, as PC1 plays a decisive role in the maturation of hormonal CCK in the gut, whereas PC2 governs the processing of brain proCCK.

Animals↗

PubMed1996

Conformational restriction of Tyr and Phe side chains in opioid peptides: information about preferred and bioactive side-chain topology.

The side chain of Tyr and Phe was fixed into the gauche(-) or gauche(+) conformation by using the Tic Htc structures, and into the trans conformation by using an aminobenzazepine-type (Aba) structure. When incorporated into dermorphin or deltorphin II, the Tic and Htc analogues all showed a large decrease in both mu and delta affinities and activities. Fixation of Phe(3) in the trans rotamer resulted in a large increase in delta affinity in the dermorphin analogue, whereas in the [Aba(3)-Gly(4)] deltorphin II analogue, good delta affinity is maintained despite the removal of the Glu side chain. Whereas several authors propose a gauche(-) preferred conformation for the Phe(3) side chain, these results suggest a trans conformation at the delta receptor. The use of these conformationally constrained residues for evaluating the preferred solution conformation in the flexible N-terminal tripeptide Tyr-D-Ala-Phe is illustrated. The (1)H-nmr parameters--chemical shift, temperature dependence, and nuclear Overhauser effects to the D-Ala(2) methyl protons in the different analogues--provide direct evidence to confirm the proposed sandwich conformation in the native peptides.

Amino Acid Sequence↗

PubMed1991

Antibodies to interleukin 3 as probes for the interaction of interleukin 3 with its receptor.

A series of antibodies, directed against murine interleukin-3 (IL-3) or synthetic peptides corresponding to portions of the IL-3 sequence, has been used to detect receptor-bound IL-3 on the surface of cells. An assay was developed in which the bound primary antibody was detected using a biotinylated secondary antibody and fluorescein isothiocyanate-labeled streptavidin, followed by analysis on a fluorescence-activated cell sorter. The fluorescence signal was shown to be specific for cells known to express IL-3 receptors and was dependent on the preincubation of cells with IL-3 under conditions that did not allow internalization of receptors. Antisera raised against full-length synthetic IL-3 or to the N-terminal 29 residues were found to give equivalent signals. On the other hand, antibodies to residues 91-118 showed no signal in this assay, despite being able to bind to IL-3 in solution and neutralize IL-3 bioactivity. When peptides corresponding to residues 30-43 and 123-140 were incubated with the anti-IL-3 antiserum, the majority of the fluorescence signal was abolished, indicating that these two peptides contained the primary epitopes being recognized by the antiserum in this assay. This antiserum also bound to the 91-118 peptide, but the corresponding peptide was not able to reduce the fluorescence signal in a similar competition assay. These results suggest that the 91-118 region is not accessible to antibody when IL-3 is bound to its receptor, whereas at least portions of epitopes 1-29, 30-43, and 123-140 remain accessible to antibody.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗

PubMed1986

An immunoreactive peptide in milk contains bombesin-like bioactivity.

Parallel in vitro bioassays using rat uterus and guinea pig large intestine tissues specific for the bombesin family of peptides, demonstrated that the bombesin-like peptides present in bovine milk can produce a dose-related response similar to bombesin and litorin. The bioactivity of this type of milk peptide appeared to be approximately 20-50% as active as the amphibian peptides. These data support the proposal that a bombesin immunoreactive peptide in milk contains bombesin bioactivity.

Animals↗

PubMed2006

The in vitro real-time oscillation monitoring system identifies potential entrainment factors for circadian clocks.

BACKGROUND: Circadian rhythms are endogenous, self-sustained oscillations with approximately 24-hr rhythmicity that are manifested in various physiological and metabolic processes. The circadian organization of these processes in mammals is governed by the master oscillator within the suprachiasmatic nuclei (SCN) of the hypothalamus. Recent findings revealed that circadian oscillators exist in most organs, tissues, and even in immortalized cells, and that the oscillators in peripheral tissues are likely to be coordinated by SCN, the master oscillator. Some candidates for endogenous entrainment factors have sporadically been reported, however, their details remain mainly obscure. RESULTS: We developed the in vitro real-time oscillation monitoring system (IV-ROMS) by measuring the activity of luciferase coupled to the oscillatory gene promoter using photomultiplier tubes and applied this system to screen and identify factors able to influence circadian rhythmicity. Using this IV-ROMS as the primary screening of entrainment factors for circadian clocks, we identified 12 candidates as the potential entrainment factor in a total of 299 peptides and bioactive lipids. Among them, four candidates (endothelin-1, all-trans retinoic acid, 9-cis retinoic acid, and 13-cis retinoic acid) have already been reported as the entrainment factors in vivo and in vitro. We demonstrated that one of the novel candidates, 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), a natural ligand of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma), triggers the rhythmic expression of endogenous clock genes in NIH3T3 cells. Furthermore, we showed that 15d-PGJ2 transiently induces Cry1, Cry2, and Roralpha mRNA expressions and that 15d-PGJ2-induced entrainment signaling pathway is PPAR-gamma--and MAPKs (ERK, JNK, p38MAPK)-independent. CONCLUSION: Here, we identified 15d-PGJ2 as an entrainment factor in vitro. Using our developed IV-ROMS to screen 299 compounds, we found eight novel and four known molecules to be potential entrainment factors for circadian clocks, indicating that this assay system is a powerful and useful tool in initial screenings.

Animals↗

PubMed2026

Harnessing Probiotic LAB and Bacteriocins for Clean-Label Food Processing and Biopreservation: Omics, Molecular Innovations and Industrial Applications.

The persistence of microbial agents in foods, especially spore forming bacteria is one of the most significant challenges to food preservation and safety, undermining product quality, shelf life, and consumer health. The use of traditional control methods, including thermal processing and chemical preservatives, are increasingly limited by consumer demands for minimally processed foods, and the emergence of resistant microbial strains. Advances have been made in the use of probiotics like lactic acid bacteria (LAB) and their biometabolites like bacteriocins in food processing and preservation, particularly to control biofilm and endospore forming pathogens including Bacillus sp., Listeria sp., Staphylococcus sp., Clostridium sp., E. coli etc. in foods and food processing plants/surfaces. Given the ability of these organisms to cause foodborne illness and form resilient biofilms in the food processing ecosystem and their resistance to the conventional method of their elimination, the antimicrobial peptides (bacteriocins) are gaining increasing prominence as useful alternatives to synthetic antimicrobials in enhancing food safety and combating the threats of these pathogens. This review addresses current information on the inhibition of persistent microbial spoilage contaminants, biofilm-forming pathogens, and spore formers of interest to the food industry using LAB and their bacteriocins. Current developments in isolation, characterization, and mode of action of bacteriocins are explored, including synergistic activity with other preservative hurdle techniques such as encapsulation, and nanobiotechnology. Importantly, there is a focus on the utilization of molecular and omics-based approaches to enable a better understanding of bacteriocin biosynthesis, gene regulation, host-microbe interactions and gut microbiome regulation potential of probiotic LABs, permitting the rational development of targeted and strain-specific interventions. Developments in the incorporation of bacteriocin-producing LAB into functional starter cultures and bio-protective products, and challenges in stability, regulatory approval, and scalability for industrial use, are also discussed in the paper. Despite their considerable potential, broader translation remains constrained by regulatory requirements, production and formulation costs, variable efficacy in complex food matrices, and the limited validation of many candidate bacteriocins beyond laboratory and model-food systems. Collectively, these advances position LAB and their bacteriocins at the leading edge of developing sustainable, clean-label, and efficacious functional foods and food preservation systems. Their functionality can be expanded by integrating genomics, synthetic biology, and predictive modeling for the maximization of their biopreservative potential in diverse food matrices and in gut microbiota modulation.

Bioactive Peptides↗

PubMed2000

Predominant torsional forms adopted by dipeptide conformers in solution: parameters for molecular recognition.

The present paper describes the predominant conformational forms adopted by dipeptides in aqueous solution. More than 50 dipeptides were subjected to conformational analysis using SYBYL Random Search. The resultant collections of conformers for individual dipeptides, for small groups with related side chain residues and for large groups of about 50 dipeptides were visualized graphically and analysed using a novel three-dimensional pseudo-Ramachandran plot. The distribution of conformers, weighted according to the percentage of each in the total conformer pool, was found to be restricted to nine main combinations of backbone psi (psi) and phi (phi) torsion angles. The preferred psi values were in sectors A7 (+150 degrees to +/-180 degrees), A10 (+60 degrees to +90 degrees) and A4 (-60 degrees to -90 degrees), and these were combined with preferred phi values in sectors B12 (-150 degrees to +/-180 degrees), B9 (-60 degrees to -90 degrees) and B2 (+30 degrees to +60 degrees). These combinations of psi and phi values are distinct from those found in common secondary structures of proteins. These results show that although dipeptides can each adopt many conformations in solution, each possesses a profile of common conformers that is quantifiable. A similarly weighted distribution of dipeptide conformers according to distance between amino-terminal nitrogen and carboxyl-terminal carbon shows how the preferred combinations of backbone torsional angles result in particular N-C geometries for the conformers. This approach gives insight into the important conformational parameters of dipeptides that provide the basis for their molecular recognition as substrates by widely distributed peptide transporters. It offers a basis for the rational design of peptide-based bioactive compounds able to exploit these transporters for targeting and delivery.

Computer Simulation↗

PubMed1995

Tyrosine O-sulfation promotes proteolytic processing of progastrin.

Tyrosine O-sulfation is a common post-translational modification of secretory and membrane proteins. The biological function of sulfation is known in only a few proteins, where it appears to enhance protein-protein interactions. Based on known sequences around sulfated tyrosines, a consensus sequence for prediction of target tyrosines has been proposed. However, some proteins are tyrosine sulfated at sites that deviate from the proposed consensus. Among these is progastrin. It is possible that the deviation explains the incomplete sulfation characteristic for bioactive gastrin peptides. In order to test this hypothesis, we have performed site-directed mutagenesis of the gastrin gene followed by heterologous expression in an endocrine cell line. The results show that substitution of the alanyl residue immediately N-terminal to the sulfated tyrosine with an acidic amino acid promotes the sulfation of gastrin peptides. Hence, the study supports the proposed consensus sequence for tyrosine sulfation. Importantly, however, the results also reveal that complete sulfation increases the endoproteolytic maturation of progastrin. Thus, our study suggests an additional function for tyrosine sulfation of possible general significance.

Amino Acid Sequence↗